This application is a continuation of PCT Application No. PCT/EP02/01325, filed on Feb. 8, 2002, which claims the benefit of priority to German Application No. 101 12 355.8 filed Mar. 13, 2001.
The invention relates to a method for installation of a temperature-sensitive electronic component on a board comprising providing a board which has openings for solder connections on an electronic component to pass through, providing a removable protection apparatus to protect the component during the installation process, moving the component first so close to the board that the solder connections project through the openings in the board, connecting the solder connections using a soldering method to a conductor track which is provided on a side of the board which faces away from the component, and subsequently removing the protection apparatus once the soldering process has been completed. The invention also relates to protection apparatus for a temperature-sensitive electronic optoelectronic component, for use during an installation process during which solder connections which are provided on the component are connected to a conductor track which is provided on a side of a board which faces away from the component.
Many electronic and electrical assemblies and components have temperature-sensitive electrical and/or electronic components such as heat-sensitive integrated circuits, lithium batteries, oscillator crystals and optoelectronic components. In the course of the installation of an assembly such as this, the electrical contacts that are provided on the components must be reliably connected to conductor tracks on a board and/or to electrical contacts on other components. This installation process is preferably carried out using a soldering method, in which solder connections which are provided on the component are soldered to the board. Each component in this case has a safe range for the soldering time and temperature, in which good soldered joints can be produced. At the same time, the temperature-sensitive electrical and electronic components must not be excessively heated, in order to prevent permanent damage. Heat-sensitive components are thus subject to contradictory requirements during soldering, on the one hand with the need to ensure sufficiently high soldering temperatures for soldering in the area of the solder connections while, on the other hand, keeping the temperature sufficiently low in the temperature-sensitive areas of the components that no damage occurs to the components.
In order to avoid excessive heating of temperature-sensitive components during soldering of SMD applications, U.S. Pat. No. 5,913,552 proposes that the relevant components be provided with a cover, which is placed from above over the components to be soldered. This cover forms a heat shield for the thermal radiation which acts on that side of the components which faces away from the board during infrared soldering or vapor phase soldering. However, a cover such as this is suitable only for the use of SMD applications in which the solder connections for the components are connected to the side of the board which faces the components using a reflow soldering method. If, on the other hand, the solder connections of the components are passed through openings in the board and are soldered to conductor tracks on the side which faces away from the component (for example by dip soldering or wave soldering), then a cover as known from this U.S. Pat. No. 5,913,552 and which is placed onto the upper face of the component which faces away from the board offers no protection whatsoever, since in this case the heat primarily acts on the component from the board side.
German Patent Document No. DE 196 07 726 A1 discloses a component for surface mounting on a printed circuit board, which is intended to be protected by a reflective metal foil, which is fitted on the component, against excessive heating, by the thermal radiation acting on it during the soldering process. Although this metal foil also protects the component against thermal radiation which acts on the component from the side which faces away from the board, it does not, however, offer any protection against thermal radiation which acts on the component from the board side.
Furthermore, a printed circuit board whose upper and lower layer are metallized is known from Japanese Patent Document No. JP 030 36796 A; the aim in this case is to improve the heat dissipation to the printed circuit board from the components which are inserted into the printed circuit board via connecting pins. However, this metallization does not provide any thermal protection for the components during high-temperature dip soldering.
In order to provide protection during soldering for a component which projects through the board, in particular a variable capacitor, it is known from German Patent Document No. DE-A 29 49 914, which forms the generic profile art in this case, for that area of the component which projects through the board to be covered by a cap; in order to protect capacitors which are intended to be accessible through an opening in the board after the soldering process, the invention also proposes that this opening be protected during the soldering process by a protection platelet, which is removed after the soldering process. Although a protection platelet such as this can protect the capacitor against heat and solder vapor acting on the lower face of the component, on the board side, and which could damage the capacitor if the opening were not covered; the platelet does not, however, offer any protection against the influence of heat which acts on all sides of the component as a result of the heat in the soldering oven or the solder bath. A protection platelet such as this can thus offer only inadequate protection for particularly temperature-sensitive components.
An object of the invention is to provide a method and a protection apparatus, by means of which a temperature-sensitive component can be protected particularly effectively against heat during the soldering process.
According to one aspect of the invention, this object is achieved by providing a method for installation of a temperature-sensitive electronic component on a board, comprising providing a board which has openings for solder connections on an electronic component to pass through, providing a removable protection apparatus to protect the component during the installation process, the component is first moved so close to the board that the solder connections project through the openings in the board, connecting the solder connections using a soldering method to a conductor track which is provided on a side of the board which faces away from the component, and subsequently removing the protection apparatus once the soldering process has been completed, wherein the component is thermally coupled to the protection apparatus during the soldering process so that some of the heat which is introduced into the solder connections during the soldering process is passed to the protection apparatus. According to another aspect of the invention this object is achieved by providing a protection apparatus for a temperature-sensitive electronic optoelectronic component, for use during an installation process during which solder connections which are provided on the component are connected to a conductor track which is provided on a side of a board which faces away from the component, wherein the protection apparatus is configured to be selectively removed from the component, wherein the protection apparatus comprises a protection sleeve which surrounds at least portions of the component, and wherein the protection apparatus can be thermally coupled to the component.
According to preferred embodiments, the component is provided during the soldering process with a removable protection apparatus having a protection sleeve which surrounds the component in places and protects it from the environmental influences during the soldering process. The protection apparatus is thermally coupled to the component, and thus results in the heat which is introduced into the component from the solder bath during the soldering process being (at least partially) dissipated to the protection apparatus. This makes it possible to considerably reduce the heating of the component interior during the soldering process, and the risk of damage to the operation of the component.
According to certain preferred embodiments of the invention, the protection apparatus is advantageously coupled to the solder connections of the component, in order that the heat which is introduced into the solder connections from the solder bath is not passed completely to the component but, instead of this, is partially dissipated via the protection apparatus.
According to certain preferred embodiments of the invention, on its inner wall which faces the component, the protection sleeve expediently has a thermally insulating material, and is provided at least in places with a coating having high thermal conductivity on its outer wall which faces away from the component. The coating on the outer wall, which has high thermal conductivity, ensures that thermal radiation which acts on the component from the outside is distributed along the outer wall of the protection sleeve, is reflected, and is thus kept away from the component. The thermally insulating material which is used for the inner wall of the protection sleeve which faces the component in this case means that any heat which is introduced into the reflective outer wall is preferably radiated outwards, and only a small proportion of it is radiated in the direction of the component. In this case, the expression “thermally insulating” means a material with low thermal conductivity, such as polyester, polyethylene, polyamide, etc.
In order to achieve a particularly good protection effect for the component against the heat which is introduced during the soldering process, the thermally conductive outer wall of the protection sleeve is thermally coupled to the component, preferably to the solder connections of the component. In consequence, some of the heat which is introduced into the solder connections from the hot solder bath during the soldering process is passed to the outer wall of the protection sleeve, and is radiated from there into the environment. This results in the soldering heat being dissipated particularly quickly, thus providing particularly effective protection for the temperature-sensitive component.
According to certain preferred embodiments of the invention, in one particularly simple refinement, the protection apparatus is formed by a closed bubble composed of a thermally insulating film, in particular a polyester film, whose wall which faces away from the component is coated with a thermally highly conductive metal (for example copper or aluminum). The bubble surrounds the component in such a way that the solder connections pass through the wall, thus ensuring that the solder connections are thermally coupled to the wall of the bubble. After the soldering process, the bubble is removed by tearing it open in the area of the solder connections; in this case, the holes which are produced by the solder connections in the bubble act as perforations to assist the tearing process.
According to certain preferred embodiments of the invention, in a further refinement, the protection apparatus is formed by an elastic clip with thermally conductive clamping edges, between whose clamping edges the protection sleeve is arranged. Before the soldering of the component, the clip is preferably attached to the component such that the solder connections of the component are clamped in between the clamping edges of the clip, and the protection sleeve surrounds the component. After completion of the soldering process, the protection apparatus is removed by releasing the clip.
According to certain preferred embodiments of the invention, wave soldering is expediently used for connecting the solder connections of the component to the board. In this method, the populated board is passed through a standing soldering wave; the speed at which it passes through the solder wave must in this case be chosen such that, on the one hand, the board and the solder connections are wetted well while, on the other hand, the thermal load on them is not excessive. The method allows heat to be supplied quickly and is thus particularly suitable for boards with plated-through holes.
Alternatively, according to certain preferred embodiments of the invention, dip soldering can also be used, in which the rear face of the board, which faces away from the component, is immersed in a bath of melted solder, and is thus wetted with solder.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.